Page:The fairy tales of science.djvu/63

 In old times these extraordinary effects would probably have been ascribed to some mischievous demon contained in the laughing gas, and the "bell, book, and candle," would have been deemed indispensable for its exorcism.

Another compound is a colourless and invisible gas so poisonous that animals plunged into it instantly expire; a third, a corrosive orange-coloured vapour, equally noxious; and a fourth, the well-known liquid called aqua-fortis, a powerful acid which dissolves copper and other metals, and which destroys all organic substances.

Such are the compounds of nitrogen and oxygen, the very elements which we draw into our lungs at every inspiration, and without which we could not exist.

Carbonic acid gas though incapable of supporting life is not poisonous, and its presence in the atmosphere does not disturb our vital functions. Animals may be drowned in pure carbonic acid, but they cannot be poisoned by it. If the atmosphere contained another compound of carbon and oxygen, namely, carbonic oxide, in place of this innocuous gas, the world would be a lifeless desert, as carbonic oxide is an active poison, and a very small quantity of it would suffice to infect the air.

The philosopher who declared that air came from the stars, figuratively expressed a great truth. We have only to examine the wondrous constitution of the gaseous mixture to be convinced that it must